Apparatus for sealing mechanical connection at bipolar barrier sheet

ABSTRACT

In a filter press cell for the electrolytic production of chlorine from aqueous alkali metal chloride solutions and having adjacent pairs of anodes and cathodes mechanically and electrically interconnected, a system is provided for connecting the foregoing electrodes while sealing out the electrolyte from the passageway through which the connection passes.

United States Patent 91 Barkel I [451 Nov. 19, 1974 APPARATUS FOR SEALING MECHANICAL CONNECTION AT BIPOLAR BARRIER SHEET Inventor: Barry M. Barkel, Saline, Mich.

BASF Wyandotte Corporatio Wyandotte, Mich.

Filed: Dec. 17, 1973 Appl. No.: 425,138

Assignee:

US. Cl 204/254, 204/255,-204/256, 204/268, 204/286 Int. Cl. a BOlk 3/10 Field of Search 204/254, 255, 256, 268, 204/286 References Cited UNITED STATES PATENTS 6/1918 MacDougall et al. 204/256 X Primary Examiner-John H. Mack Assistant Examiner-W. I. Solomon Attorney, Agent, or FirmRobert M. Phipps; Joseph D. Michaels; Bernhard R. Swick 5 Claims, 2 Drawing Figures 20 I l l APPARATUS FOR SEALING MECHANICAL CONNECTION AT BIPOLAR BARRIER SHEET BACKGROUND ACS Monograph 154, J. S. Sconce, editor, Reinhold- Publishing Company, New York, N.Y., 1962, a diaphragm-type cell has been commonly used in the production of chlorine and caustic from aqueous alkali metal chloride solutions. The filter press variant of diaphragm cells is becoming of more consequence to chlorine manufacturers. However, satisfactory electrical connection between the individual cell units, which are both compact and leakproof, continue to be sought. In

some cells the external wiring from one individual cell.

to another is objectionable. In other cells, see for instance U.S. Pat. No. 3,242,059, expensive titanium metal fabricated parts are used as both an individual cell divider and transfer electrical connection. In order to achieve satisfactory compactness and economy in a filter press cell arrangement, an efficient leakproof electrical'connection which will permit the utilization of a plastic barrier is desired.

SUMMARY OF THE INVENTION In accordance with this invention there is provided in a bipolar electrolytic filter press cell'for the production of chlorine from aqueous alkali metal chloride solutions wherein the metal anode and metal cathode of adjoining cells are in direct electrical connection with each other and said anode and cathode are maintained in spaced relationship by an electrically inactive cell wall or barrier sheet between them, the improvement of independently maintaining proper electrical and mechanical connections between the anode and cathode of adjacent cells while preventing electrolyte and gas flow through the cell barrier joint between said anode and cathode comprising in combination 1. molding said barrier sheet around at least one valve metal connector rod having a valve metal circumferential restraining flange attached thereto and positioned substantially equidistant from each end of said rod. said flange being substantially equidistant from and substantially parallel to both faces of said barrier sheet so that both ends of said rod are exposed to an electrolyte and removed from and above the face of said barrier sheet, and

. attaching to one end of said rod a metal anode and attaching to the other end of said rod a ferrous metal cap and attaching to said cap a metal cathode whereby an electrical and mechanical connection is made between the adjacent cells without danger of connector rod slippage or electrolyte leakage around said rod.

DESCRIPTION OF THE DRAWING FIG. 1 is a cutaway of the improved bipolar electrode joint and seal taken at the middle of and along the length of the connector rod joining the anode and cathode together.

FIG. 2 is an exploded view of parts comprising the apparatus of FIG. 1 prior to the molding of said parts into the apparatus of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT In this invention as shown in FIG. 1, a typical bipolar electrolytic cell for the manufacture of chlorine and caustic is equipped with a metal anode 30, a plastic barrier sheet 10 or cell wall, which is electrically nonconductive and chemically inert when the cell is in operation, between adjacent cells of the filter press and the metal cathode 26 of the adjacent cell. Electrical and mechanical connection and support between anode 30 and cathode 26 is provided by a valve metal connector rod assembly 16 including circumferential valve metal flange 20 attached substantially equally distant from each end of the connector rod 18 and equidistant from each face of, and parallel to each face of, the barrier sheet 10. For convenience the connector 1 rod 18 can have thread engaging means, e.g., threaded,

so that the cathode attaching cap 28 can be attached in a mechanical connection to connector rod 18 by thread engaging means although the cap can be attached by other permanent means, e.g., welding. The cathode 26 which is typically made of a ferrous metal, e.g., iron or steel, is mounted, e.g., by welding it to the cathode attaching cap 28 after the cap is installed. The anode 30 which typically is made of a valve metal is directly attached, e.g., welded, to the connector rod 18. To those of ordinary skill in the cell construction and operation art, it will be readily apparent that greater alignment of cathode 26 and anode 30 as well as improved electrical current distribution can be obtained by the use of two or more, three being a suitable num: ber, connector rods 16 per barrier sheet 10 depending upon the size of the cell.

FIG. 2 in exploded view shows the various parts of the invented apparatus prior to molding into a unit. Connector rod assembly 16 consists of a connector rod 18 to which a circumferential flange 20 is welded 22 substantially equidistant from each end of connector rod 18. Barrier sheet 10 consists of two half-sheets l2,

14 of the same thickness, each having an aperture 15 substantially of size to receive connector rod 18. One sheet 12, 14 is placed on each side of the connector rod assembly 16. So as to insure sufficient thermoplastic material to seal the connector rod assembly 16, a thermoplastic sleeve (for the connector rod) 24 is fitted over each end of the connector rod 18 while insuring that after molding the ends of connector 18 will remain exposed. Conventional means of loading and operating the mold are employed in fabricating the barrier sheet with the electrical and mechanical connector of this invention.

Alternatively, the invention as shown in FIG. 1 can be prepared in a one-step molding method wherein by the use of unmolded loose particle thermoplastic material the separate molding of half sheets 12, 14 are avoided. In this method the rod assembly 16 as required is appropriately positioned in the mold, the mold closed, heated to molding temperature, charged with the loose particle thermoplastic material and then molded in the conventional manner. The choice of method by which to manufacture products of this invention depends on factors beyond the scope of this invention. Among these factors are labor supply, molding and materials handling equipment available, and the particular molding characteristics of the thermoplastic material being utilized. Either method can produce satisfactory products of this invention.

The barrier sheet 10, or combined barrier sheet 10, and frame (not shown) is constructed of a chemically inert and electrically non-conducting thermoplastic material such as polyolefin derived from an olefin containing 2 to 4 carbon atoms including polyethylene, polypropylene, polybutene-l and mixtures thereof; polytetrafiuoroethylene, polyvinylidene fluoride polymers and acrylonitrile butadiene styrene terpolymers.

' The properties of these polymers are improved by adding inert, non-conducting yet reinforcing fillers such as asbestos or glass fibers, mica, kaolin or carbon black. An exemplary composition for use in this invention is an asbestos filled polypropylene composition, e.g., as disclosed in British Pat. No. 1,246,034 which for the sake of brevity is incorporated herein by reference.

Both the anode 30 and cathode 26 can be either a solid metal sheet, a woven wire arrangement or an expanded metal mesh as desired, the configuration of the electrodes being beyond the scope of the present invention.

By valve metals it is meant metals of tungsten, titanium, zirconium, tantulum and niobium. Preferably, titanium or tantulum is employed and it is normally a commercially pu're grade such as electrolytic grade. Alloys of valve metals can be employed as long as the alloy meets the criterion of passivity, metal alloys which become passivated when polarized anodically can remain passive well beyond the anodic potential needed to convert a chloride ion to chlorine. The phenomenon of passivity in this connection is discussed in an article by Greene appearing in the April 1962 issue of Corrosion, pages 136-! to l42-t, wherein reference may be made to FIG. 1 of the article which describes typical active-passive transition of a metal towards a corrosive medium. Titanium alloys of aluminum, vanadium, palladium, chromium or tin can be employed in which the latter metals are present as less than perium and palladium and alloys of two or more of the foregoing metals. Many means for applying and the formulations of platinum group metals and compounds for these coatings are known, for instance, see US. Pat.

Nos. 3,632,498; 3,630,768; 3,616,446; 3,242,059; and 3,177,131 which for the sake of brevity are incorporated herein by reference.

Many other modifications and ramifications will naturally suggest themselves to those skilled in the art based on this disclosure. These ramifications and modifications are intended to be comprehended as within the scope of this invention. I

Having thus described the invention, what it is desired to claim and secure by Letters Patent is:

1. In a bipolar diaphragm electrolytic filter press cell for the production of chlorine from aqueous alkali metal chloride solutions wherein the metal anode and metal cathode of adjoining cells are in direct electrical connection with each other and said anode and cathode are maintained in spaced relationship by an electrically inactive barrier sheet between them, the improvement of independently maintaining proper electrical and mechanical connections between the anode and cathode of adjacent cells while preventing electrolyte and gas flow through the cell barrier joint between said anode and cathode comprising in combination 1. said barrier sheet being molded around at least one valve metal connector rod, said connector rod having a valve metal circumferential restraining flange attached thereto and positioned substantially equidistant from each end of said rod, said flange being substantially equidistant from and substantially parallel to both faces of said barrier sheet so that both ends of said rod are exposed to an electrolyte and removed from the face of said barrier sheet, and

2. said rod having attached to one of its ends a metal anode and having attached to the other end of said rod a ferrous metal cap, with a metal cathode attached to said cap whereby an electrical and mechanical connection is made between adjacent cells without danger of connector rod slippage or electrolyte leakage around said rod.

2. The improvement of claiml wherein the ferrous metal cap is attached to the connector rod by thread engaging means.

3. The improvement of claim 1 wherein the anode is attached to said rod and the cathode is attached to said cap by welding.

4. The improvement of claim 1 wherein the valve metal is titanium.

5. The improvement of claim 1 wherein the anode is coated with at least one platinum group metal or metal compound. 

1. IN A BIPOLAR DIAPHRAGN ELECTROLYTIC FILTER PRESS CELL FOR THE PRODUCTION OF CHLORINE FROM AQUEOUS ALKALI METAL CHLORIDE SOLUTIONS WHEREIN THE METAL ANODE AND METAL CATHODE OF ADJOINING CELLS ARE IN DIRECT ELECTRICAL CONNECTION WITH EACH OTHER AND SAID ANODE AND CATHODE ARE MAINTAINED IN SPACED RELATIONSHIP BY AN ELECTRICALLY INACTIVE BARRIER SHEET BETWEEN THEM, THE IMPROVEMENT OF INDEPENDENTLY MAINTAINING PROPER ELECTRICAL AND MECHANICAL CONNECTIONS BETWEEN THE ANODE AND CATHODE OF ADJACENT CELLS WHILE PREVENTING ELECTROLYTE AND GAS FLOW THROUGH THE CELL BARRIER JOINT BETWEEN SAID ANNODE AND CATHODE COMPRISING IN COMBINATION
 1. SAID BARRIER SHEET BEING MOLDED AROUND AT LEAST ONE VALVE METAL CONNECTOR ROD, SAID CONNECTOR ROD HAVING A VALVE METAL CIRCUMFERENTIAL RESTRAINING FLANGE ATTACHED THERETO
 2. SAID ROD HAVING ATTACHED TO ONE OF ITS ENDS A METAL NODE AND HAVING ATTACHED TO THE OTHER END OF SAID ROD A FERROUS METAL CAP, WITH A METAL CATHODE ATTACHED TO SAID CAP WHEREBY AN ELECTRICAL AND MECHANICAL CONNECTION IS MADE BETWEEN ADJACENT CELLS WITHOUT DANGER OF CONNECTOR ROD SLIPPAGE OR ELECTROLYTE LEAKAGE AROUND SAID ROD.
 2. said rod having attached to one of its ends a metal anode and having attached to the other end of said rod a ferrous metal cap, with a metal cathode attached to said cap whereby an electrical and mechAnical connection is made between adjacent cells without danger of connector rod slippage or electrolyte leakage around said rod.
 2. The improvement of claim 1 wherein the ferrous metal cap is attached to the connector rod by thread engaging means.
 3. The improvement of claim 1 wherein the anode is attached to said rod and the cathode is attached to said cap by welding.
 4. The improvement of claim 1 wherein the valve metal is titanium.
 5. The improvement of claim 1 wherein the anode is coated with at least one platinum group metal or metal compound. 